Current filamentation in astrophysical magnetohydrodynamic jets

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Abstract
Astrophysical plasmas typically have to be considered as highly collision-free from a kinetic point of view or highly ideal in a fluid description. This refers to near-Earth space plasmas, like the magnetosphere, or extragalactic objects like radio jets, as well. On the other hand, magnetic reconnection is discussed to play an important role as an effective mechanism for conversion of magnetic energy into kinetic energy by particle acceleration. As magnetic reconnection demands for local deviations from adiabatic plasma conditions, in the highly collision-free plasma regime inertia driven reconnection should be expected. In the framework of a magnetohydrodynamic description, anomalous resistivity due to current driven microinstabilities is discussed to provide sufficient nonidealness. Both classes of processes demand for sufficiently thin current sheets. This constraint can be fulfilled by current filamentation. In the present paper numerical magnetohydrodynamical studies are used to show that ideal boundary perturbations (like, e.g., Kelvin–Helmholtz modes) can result in filamentary current structures. This fundamental process is discussed with respect to extragalactic jets.